The following list, prepared three years ago by David Walsh after the shooting at the Navy Yard in Washington DC that took 12 lives, focuses on shootings by lone gunmen. #1 would now be the Orlando shooting by Omar Mateen on June 12, 2016 that took 49 lives. (Nota Bene: In the wake of the Orlando shooting the media received criticism for saying this was the worst mass shooting in American history. Critics objected that the list should also include the attack on pioneers killed by Mormons in 1857 that left 120 dead, the Wounded Knee Massacre that took the lives of some 300 Native American men, women and children, among others.)

The Bath School disaster remains the deadliest mass killing in
American history. On May 18, 1927, Andrew Philip Kehoe, a farmer,
engineer, and sometime elected official in Bath Township, Michigan,
murdered his wife, fire bombed his own house, bombed the Bath
Consolidated School – killing thirty-eight people in one fell swoop
– then drove to the school in his truck and detonated a hidden bomb
in the vehicle, killing himself and several others. A total of 45
people (including Kehoe) were killed. The motive was evidently
revenge for losing an election for the position of township clerk.

Seung-Hui Cho's rampage across the Virginia Tech campus remains
the deadliest school shooting in U.S. history. Armed with two
pistols, Cho, a student at the school, shot and killed 33 people
(including himself) and wounded 23 others. Plagued by a history of
mental illness, he was earlier accused of stalking his fellow
students and was encouraged by his English professor to seek
counseling. Cho's motive remains unknown.

After murdering his mother and taking her Bushmaster XM15-E2S
rifle, based on the AR-15 semiautomatic rifle (the M-16 rifle issued
to U.S. soldiers is a variant) Adam Lanza stormed into Sandy Hook
Elementary School, gunning down 26 people before turning his weapon
on himself. Most of the dead were first-grade students. The exact
motive remains unknown, though Lanza had a history of mental
disorders.

George Hennard, armed with two semiautomatic pistols, drove his
pickup truck through the front window of a Luby's restaurant, then
took his weapons and shot and killed 23 people, wounding 20 morning,
then committing suicide. Hennard had a criminal record for drug
possession, struggled with depression, and frequent expressed his
hatred of women. Police speculated that Hennard's misogyny was an
irrational hatred of women – 14 of the 23 people he killed were
women.

James Oliver Huberty walked into a McDonald's in the San Ysidro
neighborhood of San Diego armed with a semiautomatic Uzi 9mm, a
pump-action shotgun, and a semiautomatic pistol. He killed 22 people
and wounded 19 more before being shot and killed by a police sniper.
His exact motive for the attack remains unknown, though most of his
victims were Mexican Americans.

Charles Whitman, a former Marine who lived in Austin, Texas,
murdered his wife and mother as part of a planned murder-suicide,
then drove to a hardware store to purchase a semiautomatic carbine
and a shotgun, along with ammo boxes. He returned home to load his
new purchases, along with survival gear and several other firearms,
before driving to the University of Texas campus, barricaded himself
in the campus clocktower, and open fire on passersby below. A total
of 17 people died that day, including Whitman himself.

The phrase “going postal” originates from Patrick Sherrill's
attack on his workplace, a U.S. Post Office in Edmond, Oklahoma.
Sherrill, a relief letter carrier, first killed his supervisor, who
had earlier discipline Sherrill, then stalked and killed 13 other
co-workers before committing suicide.